The mechanisms by which animals respond to environmental temperature is not fully understood. C. elegans responds to ambient temperature in a complex, experience-dependent manner. The behavior of C. elegans on a thermal gradient is dependent on its prior temperature history. The goal of this proposal is to define the molecular and neuronal mechanisms required for C. elegans thermosensory responses and behavioral plasticity. Specifically, we will: 1) Characterize the molecules and pathways in the AFD thermosensory neurons required for different aspects of C. elegans thermosensory behavior. We have used quantitative behavioral and calcium imaging assays to dissect C. elegans thermosensory behavior into several underlying components. We will use these assays to define the contributions of candidate molecules to different aspects of thermosensory responses, and begin to place these molecules in genetic and biochemical pathways. 2) Identify the thermosensory neuron driving a cryophilic bias. Neuronal circuit analyses indicate that a thermosensory neuron other than the AFD neurons responds to temperature. We will identify this neuron using laser-mediated disruption experiments. 3) Identify and analyze molecular thermosensors. We will use forward and reverse genetic approaches to identify molecular thermoreceptors. Thermoreceptor functions will be further validated by misexpression and heterologous expression experiments. This work will identify new molecules involved in thermosensation, thermosensory signal transduction and neuronal plasticity. We expect that similar molecules and mechanisms operate in higher animals to regulate nervous system function in multiple contexts, including in neuronal disorders. Lay summary: The goal is to identify molecules and neurons required for sensing temperature using the C. elegans model system. Many of these genes are expected to be conserved in other organisms including humans, and to play important roles in regulating neuron functions.